1. Field of the Invention
This invention relates to an electrostatic chuck for holding an object to be processed, such as a wafer, by means of coulombic energy, and also to a plasma etching apparatus equipped with the electrostatic chuck.
2. Description of the Related Art
An electrostatic chuck holds an object such as a wafer by utilizing the coulombic energy of those negative and positive electric charges on the object and an electrode which are created by applying voltage between the object and the electrode arranged with an insulating layer interposed therebetween.
An electrostatic chuck of this type has been proposed which has an electrostatic holding member interposed between a chuck main body and a wafer. This member is connected to a band-like power supply member covering the side and rear surfaces of the chuck body. If the surface of the chuck body is circular, the electrostatic holding member is formed circular to accord with the chuck body. Each of the members comprises two polyimide insulating member and a conductive member made of copper, etc., and interposed between the insulating members, thus being flexible.
Further, there exists another electrostatic chuck comprising a ceramic chuck body, a conductive member arranged in parallel with a wafer, and a power supply pin perpendicularly inserted in the body from the rear side thereof, for supplying power to the conductive member.
In a plasma etching apparatus, wafers are cooled so as not to be deformed due to high temperature caused by plasma during occurrence thereof. In general, the table is cooled in order to cool a wafer placed thereon. For performing effective heat transfer between the table and wafer, it is necessary to bring the wafer into tight contact with the table. Since they are usually kept in contact by clamping, it is hard to obtain uniform contact. Using an electrostatic chuck is very effective in this case.
The largest problem of the first-mentioned electrostatic chuck is that part of the power supply member extends into the wafer-processing chamber. If this chuck is employed in a plasma etching apparatus, the extended portion of the member will inevitably be damaged by plasma. Even if a tubular crystal cover is provided over the extended portion, plasma may be guided through a clearance formed between the crystal cover and a wafer, damaging the power supply member, thus greatly shortening its life.
On the other hand, in the latter electrostatic chuck, the power supply pin is free from damage due to plasma. However, since the pin is projected upward to mechanically and electrically contact the conductive member, thereby raising the surface of the chuck on which a wafer is to be placed, the electrostatically holding force exerted on the wafer may be reduced.